1. FIELD OF THE INVENTION
The present invention generally relates to a refrigerating apparatus and more particularly to a refrigerating apparatus provided with a hot gas bypass circuit for allowing a coolant gas of high temperature and high pressure to be selectively supplied to an evaporator constituting a part of the refrigerator.
2. PRIOR ART
Referring to FIG. 4 of the accompanying drawings, there is shown a typical conventional circuit arrangement of a refrigerating apparatus, wherein a gas coolant is compressed to a high temperature and a high pressure by a compressor 01 to be subsequently fed to a condenser 03 where the gas coolant is cooled by a fan 015 mounted externally. The coolant thus condensed is then expanded by an expansion valve 06 and subsequently evaporated by an evaporator 07 while absorbing external heat. The coolant leaving the evaporator 07 is circulated back to the compressor 01. In a practical application, the evaporator 07 may be employed as a cooler, for example, in an ice making machine. In that case, a hot gas (gas coolant) of a high temperature is supplied directly to the evaporator 07 by opening a hot gas bypass valve 011 during a defrosting or deicing operation mode of the ice making machine. In FIG. 4, reference numeral 09 designates an accumulator, and numeral 08 designates a check valve which serves to prevent the backflow of the coolant of high temperature and high pressure leaking from the compressor 01 to the evaporator 07.
In a refrigeration apparatus disclosed in Japanese Laid-Open Patent Application No. 73259/1985 (JP-A No. 60-73259), there is provided a gas circuit extending around a condenser and including a check valve similar to the check valve 08 shown in FIG. 4, although the hot gas bypass circuit of the type mentioned above is not incorporated. The gas circuit of this known refrigeration apparatus is designed to serve rapidly eliminating the pressure difference across the compressor upon stoppage thereof.
Turning back to FIG. 4, it is assumed that the refrigerating apparatus is used in combination with an ice making machine. When the operation of the compressor is stopped during an ice making operation due to an interruption of power supply, it is a common practice to restart the operation of the ice making machine from the hot gas bypass mode (i.e. deicing or defrosting cycle) in order to prevent twofold formation of ice and shortage of raw water. In this connection, it is noted that the attempt for restarting the ice making apparatus within the shortest possible time after restoration of power is accompanied with problems mentioned below. Upon interruption of power, the condenser will remain in a high temperature and high pressure state for a while. Accordingly, when the hot gas valve is opened to restart the operation of the ice making machine as soon as power is restored within a short time after the interruption, a large amount of coolant will then flow into the evaporator from the condenser together with the coolant gas discharged from the compressor. The large amount of gas coolant flowing into the evaporator is cooled to such extent that the gas-phase coolant and the liquid-phase coolant coexist in a mixed state. The gas and liquid mixture of the coolant will then flow into the accumulator. In that case, the liquid-phase coolant may often overflow from the accumulator into the compressor, causing damage to the latter. Further, if a rotary compressor is employed, the liquid-phase coolant flowing into the compressor will subsequently undergo compression, resulting in failure in the restarting operation.
Also, in order to realize a smooth restart of the compressor, the pressures of coolant in the discharge port and in the suction port of the compressor have to be balanced with each other at the earliest possible time. This requirement can not be satisfied with the structure of the refrigeration apparatus disclosed in JP-A No. 60-73259 mentioned above particularly when accumulators and compressors of large capacity are employed. In other words, a lot of time must be consumed for realizing the balance in pressure mentioned above. This can be explained mainly by the fact that the use of a large diameter pipe as well as employment of the accumulator involves a corresponding increase in the volume of the system as a whole, whereby increasing pressure in a low pressure region is accompanied with a remarkable time lag, while lowering of pressure in a high pressure region on the other hand is delayed because of a large amount of coolant existing in such region.
Furthermore, FIG. 5 shows a typical example of a prior art refrigerating circuit adopted in refrigerating devices, such as, for example, ice making machines in which the evaporator is employed for the freezing or icing operation.
In FIG. 5, a coolant of high temperature and high pressure discharged from a compressor 01 is cooled while flowing through a condenser 03 to be ultimately transformed into liquid of high pressure before being introduced into a receiver tank 05. The coolant flowing into the evaporator 07 through an expansion valve 06 is evaporated, absorbing external heat, as the result of which ice is formed on an ice making plate (not shown) disposed on the evaporator 07. The evaporated coolant gas is then circulated back to the compressor 01 through an accumulator 09. At that time, a part of the liquid coolant of high pressure and low temperature flows into the accumulator 09 through a liquid bypass circuit 030 to be mixed with the gas coolant, whereby the temperature of the latter is lowered. In this manner, the compressor 01 is maintained at a proper temperature.
In the defrosting or deicing process for removing the ice thus formed, a hot gas valve 011 is opened to supply a hot gas directly to the evaporator 07. When the hot gas valve 011 is opened to this end in the deicing process, the gas coolant of high pressure discharged from the compressor 01 flows into the evaporator 07 in an increased amount, being added with the coolant of high pressure from the condenser 03. The gas coolant is then cooled within the evaporator 07 due to the contact with the ice forming plate on which ice is formed. Thus, the coolant assumes a gas/liquid-mixed phase to be subsequently fed into the accumulator 09, as the result of which the liquid coolant level within the accumulator 09 is disturbed significantly. In such a situation, the accumulator can accommodate only a small amount of liquid coolant notwithstanding a relatively large capcity thereof. Consequently, a part of the liquid coolant may overflow into the compressor 01 to be compressed in the liquid state. This phenomenon is likely to incur damage to the compressor 01. In case the compressor 01 is of a rotary type, a so-called liquid backflow will take place to force out lubrication oil, which of course adversely affects the bearings or like parts.